Lead refining



Patented Aug. 27, 1929.

UNITED STATES 1,726,346 PATE BRUCE WINFRED eonsnn, or woonnnmen, NEW JERSEY, Ann CALVIN w. HAFIEY,

or SELBY, CALIFQRNIA, AssIGNons TO AMERICAN SMELTING AND nnrmms com:- PANY, on NEW YORK, N. Y., A CORPORATION on NEW JERSEY.

LEAD nnrmme.

No Drawing.

This invention relates to the separation of antimony and tin from leadbullion, and more particularly to a new and improved method for concentrating the tin skim which is produced by heating lead bullion and for I thereof which must be removed prior to treatment for the elimination of antimony.

This skim may contain portions of lead and antimony which must be separated there from by subsequent treatment.

When further heat is applied after the tin skim is removed the antimony is oxidized and a portion thereof passes oil in the form of agfume, whereas various other portions form a stable oxide which remains upon the surface of the bath as an antimony oxide skim which must be removed from the bath and further treated for the separation of lead.

This invention relates particularly to the concentration of the tin in the tin skim formed in treating the lead bullion and the elimination of lead and antimony and vari ous other substances therefrom. The invention also provides for the elimination of substantially the entire antimony content in the form of a fume with the formation of only a comparatively small amount of antimony oxide skim which may be taken ofi' and retreated in a subsequent bath.

The process is based upon the fact that the various oxides composing the above mentioned skims may be reduced by a suitable reducing agent with the formation of either a lower oxide or the metal itself. The reducing conditions are maintained such that a part or most of the lead or antimony which may be present in the tin skim is reduced to the metallic state and again enters the bath,

leaving the tin oxide in a more concentrated condition and forming substantially the entire skim. This action is further made use of in reducing the quantity of antimony skim by causing lower oxides of antimony to be formed which are readily volatilized and removed as fume, or by reducing the oxides to the metallic form.

The invention provides :for greatly in- Application filed February 15, 1928. Serial No. 254,606.

creasing thev efficiency of antimonylead sep aration by treating the material under alternately oxidizing and reducing conditions in order to volatilize a greater percentage of theantimony with less production of skims than has heretofore been mechanically practica v The invention further consists in the new and novel features of operation and the new and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims. Although the novel features which are be-' lieved' tobe characteristic of this invention will be particularly pointed out in. the claims appended hereto, the invention itself, as to its objects and'advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description in which a particular commercial embodiment thereof isdisclosed It will be understood however, that the proc- NT OFFICE.

esses and the steps thereof may bemodified in various respects without departing from the broad spirit and scope of the invention.

In the following description and'in the claims the various steps in the process and the details comprising the invention will be identified by specific names for convenience but they are intended to be as generic in their application as the art will. permit.-

The process in accordance with the present invention may be carried out by heating lead bullion or alloy containing antimony and tin with or without various other impurities such as copper, arsenic, bismuth, gold and silver 9'0 to a sufficiently high temperature to melt the bullion and maintaining an oxidizing atmosphere, whereby tin is oxidized and forms a skim. A suitable reducing agent is then added to the skim whereby the oxides of 311- timony and lead which may be enmeshed with the tin skim are reduced to the metallic state and re-enter the bath.

The skim which is considerably reduced in quantity by this means may then be removed and the process continued by raising the bullion to a suitable heat in an oxidizing atmosphere for the oxidation of the antimony, a portion of which will be passed off as a fume and may be recovered by suitable means, and

another portion of which forms a skim composed essentially of lead antimony oxides on the surface of the bath. The skim is then sub,-

I fjetd to a reducing condition ,untilgreater portion of the antimony oxides havebeen re duced to a volatile form which passes'otl as a fume. The treatment is then continued, preferably by alternating the reducing and oxidizing steps until the antimony content has been reduced to the desired'value. The final skim which will be comparatively small may then be removed, and returned to a subsequent bath for further treatment.

As a more specific example, the process may be carried on by melting lead bullion or al- 10y containing, forexample, percent of an- "timony and 5 percent of tin together with smaller percentages of various other impun ties such as copper, arsenic, bismuth, gold I and silver, and raising the temperature very rapidly to a bright red heat while maintaining an oxidizing atmosphere. The temperature may range from 1200 to 1800ydegrees reoxidize it while lead and, to a lesser degree,

antimony are quite easy to reduce or more difiicult to reoxidize this reduction treatment concentrates the tin without reducing any appreciable; amount to metal.

After removal of part or all of the tin, antimony volatilizes or fumesrapidly and a skim of lead and antimony oxides appears.

. lVhenever this skim becomes sufiiciently great or for any reason appears to hinder the mainly in'skims which may subsequently be free'oxidation and volatilization of antimony it is submitted to a reducing or partially "re ducing treatment as by addition of fine coke,

wherebym'uch of the antimony oxides is reduced to the volatile antimony trioxide and escapes as fume and most of the lead with some-antimony is reduced to metal.

As the operation is continued and antimony skims is not profitable. The re-- mainder of the antimony is then removed,

reduced. with a new charge of antimony-lead OPQI'SIIOH}, thefamount of antimony with? I drawn-from the furnace in skims and which Iwould re uire retreat nent to effect a separation of t e antimony and lead contained" 19F I practice.

thereinflhas been greatly reduced in actual The reactions which take place during the oxidation of metals in the bath and during 'the reduction of the slag or skim formed during the fuming operation are complex and I the metal bath becomes impoverished in. antimony. there is a greater tendency'for antimony tofbe absorbed by the bath. when 9. skim is re v 1 duced, hence there is an economic limit be-", yondwhich' the reduction treatment of the vary greatly'in importance according to the concentrations of the metals present and with furnace conditions. In what follows the course of the chief reactions will be described as they appear to occur according to present knowledge.

' During the oxidation operation both antimony and lead are oxidized by air-oxygen )ut not indirect proportion to the quantities of each present since antimony is oxidized much more readily than lead at the temperature existing in the furnace. Part of the antimony trioxide thus formed escapes as fume, part is readily oxidized still further by air to the pentoxide or to the comparatively stable tetroxide, and part remains as such with the higher oxides and litharge as a slag or skim the litharge and oxides of antimony in the slag may be combined as lead antimona'tc when cooled, the slag may be considered as being a molten mixture of separate oxides of antimony and lead as it exists in the furnaces under the usual operating conditions. skim or slag is beneficial when fluid and present in not too great a quantity as it serves as a medium for the further oxidation of antimony and largelyprevents the volatilization of lead.

The higher oxides of antimony present in the slag near the metal bath reactwith the metallic antimony to produce antimony trioxide, and part of the trioxide near the 'surface of the slag is oxidized by air to the higher oxides. Hence there occurs in eilect a transfer of air oxygen through the slag to the metallic'antimony. Lea-d oxide, which is present inthe slag, also reacts to oxidize metallic antimony and even to oxidize antimony trioxide to the higher oxides The concentration of antimony in the bath, and of each constituent in the slagas well as other factors depending upon the operating condicovering the metal bath. Although much of This tions present, determine to what extent and i with what rapidity each of the aforementioned reactions will go.

In order to increase the rate of turning of antimony, the atmosphere in the furnace is kept very oxidizingvThis tends to rapidly ioxidize antimony trioxide in the slag to the higher oxides of antimonyl Unless the concentration'of antimony in the metal bath is relatively-high, these higher oxides are not i rapidly reduced but accumulate causing a dry bearing material. By this improvement in skim which further impedes the rapidity of their reaction with the metallic bath. By partially reducing this skim, as by application of a small amount of fine petroleum coke, the higher oxides ofantimony are reduced largely to the trioxide, 'partof which'sublimes and part remains in the slag. This results in v a much smaller and a fluid slag thus greatly with oxides of antimony in the form of lead antimonate. For this reduction line low ash coke such as petroleum or pitch coke is preferred as it bath, reacts essentially as does antimony,-

that is, part of the arsenic present in the skim or sla is volatilized and part reduced to metal by the reducing treatment. Since the percentage of arsenic present is generally very small, a relatively greater amount is reduced to metal and rejoins the metal bath than is the case with antimony.

The temperature of the metal bath during the lead-antimony separation as described may range from 1200 to 1800 degrees F. and many either be held constant at some fixed temperature or intermittently be raisedand lowered.

By reducing the quantity of skim the re treatment necessary to recover and separate the metals contained therein is simplified and the expense and delay in removing the skims are minimized. In carrying on the process the character of the conditions in the furnace may be made strongly oxidizing for the oxidation and fuming of ant i'nony, and then changed to reducing in order to treat the skims or slag which may form in the manner above described. Not only is the amount of skim which must be removed from the bath considerably reduced but the rate of volatilization of the antimony is increased.

The concentration of the tin skim by removing lead and antimony therefrom simplifies the subsequent treatment for the removal of these elements and considerably reduces the quantity of material handled.

Although certain novel features of the in vention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the several steps of the process and in its operation may be made by those skilled in the art Without departing from the spirit of the invention.-

llhat is claimed is: i

1. The process of recovering antimony from lead containing said antimony in comparatively large percent-ages which comprises rap idly heating said lead to a comparatively high temperature and alternately subjecting the bath to oxidizing and reducing conditions whereby volatile oxides of antimony are formed and passed oil as a fume, and whereby non-volatile oxides which form a skim on tlfi surface of the bullion are red need to 21 volatile state. 1

2. The process of treating lead bullion containing antimony, tin and other impurities which" o jm'p'rises rapidly heating said bull on to adngh temperature whereby a tin skim is formed thereon, subjecting said skim to re ducing conditions whereby antimony and lead oxides contained therein are partially reduced to the metallic state and re-enter the bath, removing said skim and recovering tin therefrom. e I Y 3. The process of treating lead bullion containing antimony, tin and other impurities which comprises rapidly heating said bullion to a temperature of from 1200 to 1800 degrees F. whereby tin skim is formed thereon, subjecting said skim to reducing conditions whereby antimony and lead oxides contained therein are reduced to the metallicstate and re-enter the bath, removing said skim and re-i covering tin therefrom. v I 4. The process of treating lead bullion containing antimony, tin and other impurities which comprises rapidly heating said bullion to a high temperature whereby tin skim is formed thereon, adding finely divided coke to said skim whereby antimony and lead oxides contained therein are reduced to the metallic state and re-enter the bath, removing said skim and recovering tin therefrom.

5. The process of treating lead bullion which comprises rapidly heating said, bullion to a temperature above red heat whereby a tin skim is formed thereon, subjecting said skim to reducing conditions whereby lead and antimony contained therein are reduced to a metallic state and returned to the bath,- removing the concentrated skim, continuing theaps plication of heat under oxidizing conditionsf.

whereby volatile oxides of antimony;ware v formed and whereby a smaller proportion of non-volatile oxides are formed "and produce a skim, subjecting the skim to reducing conditions whereby the nonvolatile oxides are reduced to volatile ox1des,.and recov ermg the volatile oxides as fume.

(5. The process of treating lead bullion which con'iprises rapidly heating said bullion to a temperature above red heat whereby a tin skim is formed thereon, subjecting said skim to reducing conditions whereby lead and .antimony contained therein are reduced to a metallic state and returned to the bath, removing the concentrated skim, continuing the application of heat under oxidizing conditions whereby volatile oxides of antimony are formed and whereby a smaller proportion of non-volatile oxides are formed and produce a skim, subjecting the skim to reducing conditions whereby the non-volatile oxides are reduced to volatile oxides, recovering the volatile oxides as fume, removing the final skim from the bath and adding the same to additional quantities of lead bullion for further treatment.

7. The process of treating lead bullion which comprises rapidly heating said bullion to a temperature above red heat whereby a tin skim is formed thereon, subjecting said skim to reducing conditions whereby lead and antimony contained therein are reduced to a metallic state and returned to the bath, removing the concentrated skim, continuing the application of heat under oxidizing conditions whereby volatile oxides of antimony are formed and whereby a smaller proportion of non-volatile oxides are formed and produce a skim, subjecting the skim to reducing conditions whereby the non-volatile oxides are reduced to volatile oxides, recovering volatile oxides as fume, and continuing the treatment under alternately oxidizing and reducing conditions until substantially all of the antimony has been removed as a fume.

8. The process of treating lead bullion which comprises rapidly heating said bullion to a temperature above red heat whereby a tin skim is formed thereon, subjecting said skim to reducing conditions whereby lead and antimony contained therein are reduced to a metallic state and returned to the bath, removing the concentrated skim, continuing the application of heat under oxidizing conditions whereby volatile oxides of antimony are formed and whereby a smaller proportion of non-volatile oxides are formed and produce a skim, subjecting the skim to re ducing conditions whereby the non-volatile oxides are reduced to volatile oxides, removing volatile oxides as fume, continuing the treatment under alternately oxidizing and reducing conditions until substantially all of the antimony has been removed as a fume,'

removing the final quantity 'of remaining skim, and adding the same to additional amounts of lead bullion for further treatment.

' which form a skim, adding a reducing agent to the bullion whereby the antimony oxide skim is largely reduced to a volatile oxide of antimony, and again subjecting the bullion to oxidizing conditions for the formation of further fume.

10. The process of removing antimony from lead bullion containing antimony in comparatively large percentages, which com prises heating said bullion to a temperature above red heat, whereby a portion of the antimony is converted to a volatile oxide and removed as a fume, andfurther quantities of antimony are converted into non-volatile oxides which form a skim, adding finely divided coke to the bullion whereby the antimony oxide skim is largely reduced to a volatile oxide of antimony, and again subjecting the bullion to oxidizing conditions for the formation of further. fume.

11. T he processv of recovering tin and antimony from lead. bullion, which comprises rapidly heating said bullion to a temperature above red heat whereby a tin skim is formed, adding powdered coke tosaid bullion for reducing various oxides contained in said skim and concentrating the tin content thereof, removing said skim, further heating said bullion under oxidizing conditions for the production of volatile and non-volatile antiinony oxides, adding finely divided coke to said bullion for reducing the. non-volatile oxides to volatile oxides, and further sub jecting the bullion to oxidizing conditions for the formation of additional quantities of volatile oxides.

12. The method of recovering antimony from lead bullion, which comprises alternate-' ly subjecting said bullion to oxidizing and reducing conditions whereby lower oxides of antimony are formed and recovered as a fume.

13. The process of treating'lead bullion which comprises subjecting the bullion to oxidizing conditions for the formation of a tin skim, subjecting said skim to reducing conditions, and further treating said bullion in alternately oxidizing and reducing conditions whereby volatile and non-volatile oxides of antimony are formed and non-volatile oxides are reduced to volatile oxides.

14. The process of treating lead bullion which comprises subjecting the bullion to oxidizing conditions for the formation of a' tin skim, subjecting said skim to reducing conditions for the concentration of the tin.

content thereof, further treating said bullion in alternately oxidizing and reducing conditions whereby volatile and non-volatile oxides of antimony are formed and non-volatile oxides are reduced to volatile oxides, and recovering the volatile oxides as a fume.

In testimony whereof We have hereunto set our hands.

BRUCE VVINFRED GONSER. CALVIN TV, HAFFEY. 

